I am slightly worried that the subject of "Tor" alone will not create enough (good) questions to condone a independent SE site. It seems to me that Tor might be better discussed using a "Tor" tag on the proposed Privacy site. I could be wrong about this but it seems some other people have the same concern. In a different discussion, @Hjulle said (in comments):

Do you believe that just Tor will be able to produce enough questions to keep this running in the long run?

@Runa responded:

Yes. Tor changes all the time, with new releases, features, research, etc. I don't think we would run out of questions.

It could be true that the ever-evolving nature of the Tor software and privacy in general will cause new topics to pop-up all the time. My concern with this though is that this will likely cause many older questions to become invalid, probably quite quickly.

I use Stack Overflow frequently. Questions about programming languages and code construct are relevant for a long time because language specs don't change often. When they do change, we just introduce a new tag (e.g. java-7). If a question like this gets no attention for a year or two, it doesn't matter because it can still likely help someone, maybe someone who is working with older tech But, I find that the questions about programmer software (e.g. Visual Studio or IntelliJ IDEA) become out-of-date quickly as the software changes. When new releases come out, either new answers need to be created to older questions or new, similar questions appear just because the old answer doesn't apply to the new version. Unfortunately, software-based questions seem to be much more volatile. Here are some examples of (IMO) problematic questions/answers about software:

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Using version specific tags, and leaving the old questions alone when new versions come out.

If changes within a "major" version makes the answers of the same version obsolete, then previous answers should be either updated, or downvoted and new answers posted.

For questions that are version independent, but because of future changes become dependent on the version, previous answers should be either updated, or downvoted and new answers posted.

I am slightly worried that the subject of "Tor" alone will not create enough (good) questions to condone a independent SE site.

Well, it is very hard to predict how sites and communities turn out and things could go either way. While I do share this concern (in general) when it comes to single software specific sites, the fact that there are 134 example questions, is a good sign. This is much higher than what is seen on other proposals.

It seems to me that Tor might be better discussed using a "Tor" tag on the proposed Privacy site.

From a cursory look at the example questions on Privacy, I would disagree. Privacy is looking to be a site dealing with legal, ethical and social concerns of privacy and not technology or technical solutions. The audience of the site could even turn out to be largely non-technical.

I find that the questions about programmer software (e.g. Visual Studio or IntelliJ IDEA) become out-of-date quickly as the software changes. ... Unfortunately, software-based questions seem to be much more volatile.

I am not sure if this is a big problem. Even if software keeps evolving, making old answers obsolete, either of the ways mentioned work well to solve this problem. As most changes are version specific, tagging questions in the same manner will help to categorize and find questions easily both for old and new users.

On this site, when someone asks "How can I test the Tor configuration to prove that my setup is secure?", how will we make sure that the answer(s) are relevant 1 month, or 1 year later?

Here are some possibilities:

use tags (e.g. tor-v1 vs. tor-v2)

This would be a workable approach.

delete questions if they are no longer valid

Not at all! Every answer is the result of effort on someone's part, deleting old answers would be a total waste of the effort.

down-vote old, out-of-date answers and add up-to-date answers to get voted up

This is also a workable solution for version-independent questions, and is frequently seen on Stack Overflow. This is suited to questions which, at the time of posting, are not version-specific, but certain changes in future releases implicitly make the problem version-dependent.

leave them alone; maybe someone is using an older version and the info is still applicable to them?

Bundled with version tags, this is the best way to go about it.

Are there any other good SE sites which focus purely on frequently changing software products? If so, what can we learn from them on how to combat this (perceived) problem?

I agree with most, except the part about downvoting obsolete answers of minor version upgrades. If a patch fixed an issue with Java 7.0, and the recommended solution was to upgrade to Java 7.1, are the workarounds for v7.0 in an answer any less relevant for those that can't upgrade (for whatever reason)? Your first suggestion (to update answers) is what we should do. In the Java case, we would simply add something like: "This has been fixed in Java 7.1, the recommended solution is to upgrade to that version" to the top of the answer, leaving the v7.0 solution below it.
– RobotnikAug 30 '13 at 1:48

Tor is always adapting to new threats, yes, but by and large I think most of the advice surrounding it remains relatively stable over relatively long periods of time. I don't know that there is really a problem to solve here. Only time will tell.

There seems to be a contradiction here. According to the OP (to quote the quote)

Yes. Tor changes all the time, with new releases, features, research, etc. I don't think we would run out of questions.

but according to @Magnus919's answer

Tor is always adapting to new threats, yes, but by and large I think most of the advice surrounding it remains relatively stable over relatively long periods of time.

To state the obvious, this means that while Tor's internals change, high-level functionality remains the same.

If the site focuses on the high-level aspect it should be treated as a proposal for a specific software platform. If it focuses on the internals, questions will become invalid quickly.

This is especially dangerous in Tor's case because duplicate questions are frowned upon. So if some internal changes and someone in need of Tor relies upon the outdated question here, it could put him/her in a dangerous situation. Therefore the Q&A format endorsed by SE does not play to the strengths of a site specific to Tor.

Tor's mailing lists seem a much more reliable resource. Furthermore Security.SE already accepts questions regarding Tor. In my opinion the Tor proposal is a subset of, and should be "swallowed" by Security.SE.